1. Field of the Invention
The present invention relates to a mobile station position estimation scheme for estimating a position of a mobile station in a cellular mobile communication system for carrying out communications between a mobile station and base stations, and a base station device and a mobile station device for realizing this mobile station position estimation scheme.
2. Description of the Background Art
In the conventional cellular mobile communication system, it has been impossible to estimate a position of a mobile station in communication state, and for this reason it has been pointed out that there is a problem that a position of a source of an emergency call (such as dial "110" and "119" in Japan, dial "911" in U.S.A.) cannot be identified.
There are well known radio based techniques for estimating a position such as the radio navigation schemes for airplanes and ships (beacon, loran, microwave landing system, etc.). However, these techniques are not suitable for the cellular mobile communications.
Namely, the beacon requires a radar on a mobile station device so that it is not suitable for compact implementation of a mobile station device. The hyperbolic line of position scheme such as loran requires synchronization among base stations. In general, base stations of the cellular mobile communications are not synchronized with each other so that this scheme is not applicable to the cellular mobile communications, except for the IS-95 scheme of the American ELA/TIA standard which has synchronization among base stations. The microwave landing system can measure a position of an airplane within a particular area at high precision by using a special directional antenna, but it is difficult to measure an arbitrary position of a mobile station by using a simple radio equipment.
Recently, the position measurement scheme called GPS (Global Positioning System) that utilizes satellite has become popular, but this is also a system that requires high precision synchronization among satellite stations, and therefore it is applicable only to the IS-95 scheme mentioned above, and not applicable to the general cellular mobile communication systems which are asynchronous systems.
Thus there has been a problem that the conventionally known radio based position estimation techniques are not suitable for the general cellular mobile communications because the compact implementation of a mobile station device or a radio device of a base station becomes difficult and the synchronization among base stations is required.